Ride a heavily loaded tandem bicycle across several 15,000 foot passes and innumerable others at slightly lower levels. Then eat mostly rice and noodles, and get sick of both!
I weigh the same as I did in High School, but about fifteen pounds of muscle have just disappeared! The loose skin bothers me, but I am now on a concerted effort to eat as much of anything as possible and in particular protein. Wish me luck!